1. Field of the Invention
This invention generally relates to cardiac arrhythmia treatment. In particular, the present invention relates to an implantable device for preventing clotting during atrial fibrillation.
2. Description of Related Art
Atrial fibrillation is probably the most common cardiac arrhythmia. While atrial fibrillation is not acutely life threatening, it is a major cause of hospitalization. Atrial fibrillation causes a lack of blood output from the atria which may lead to blood clots in the atria due to areas of stagnant blood flow. These blood clots may break loose and can then lodge in either the lungs, if they come from the right atrium, or in the brain causing a stroke or death if they come from the left atrium. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart and may experience dizziness or even loss of consciousness. It is estimated that approximately fifteen percent of all elderly people experience atrial fibrillation.
Various types of oral drugs have been tried to treat atrial fibrillation. While some patients are helped by only drug therapies, the majority of patients are not successfully and safely treated with drugs and require a different type of treatment. One of the most significant shortcomings of these drugs is the side effects they may have on the patients. Specifically, in some patients, administration of these drugs leads to ventricular fibrillation which is almost always immediately fatal.
Unfortunately, atrial fibrillation may often be corrected only by a discharge of electrical energy to the heart. This type of treatment is generally referred to as cardioversion. There are many known external devices for applying cardioversion shocks to control atrial fibrillation. For example, U.S. Pat. Nos. 4,572,191 and 3,952,750 disclose a stand-by electrical shock device for atrial fibrillation. The external shocks are typically very painful and, unfortunately, often result in temporary relief for patients, sometimes lasting only a few weeks. Additionally, recently issued U.S. Pat. Nos. 5,282,837; 5,265,600; and 5,391,185 disclose various embodiments relating to implantable electrical atrial defibrillators.
Use of an electrical shock to stop atrial fibrillation poses some hitherto unresolved problems. Primarily, electrical atrial defibrillation requires shocks in the order of 1-2 Joules of electrical energy. Patients are typically conscious during atrial fibrillation and shocks of the magnitude of 1-2 Joules are very painful to the patient and are thus undesirable. Another significant disadvantage of electrical shock therapy is the fact that atrial defibrillation shock may lead to ventricular fibrillation. This is because a moderate level shock during the repolarization of the ventricles will typically lead to fibrillation. In order to avoid this problem, the prior art utilizes methods and apparatus to sense the R-wave in the right ventricle and to carefully synchronize the atrial shock to avoid impinging upon the ventricular T-wave which would represent the repolarization of the ventricle. The risk of fibrillating the heart with an atrial defibrillation shock can also be minimized by delivering shocks which are timed with ventricular activity. This method is generally disclosed in U.S. Pat. Nos. 5,207,219; 5,350,402; and 5,411,524.
In spite of the advances made by the prior art, atrial defibrillation shock therapy may cause ventricular fibrillation and therefore therapy for an otherwise non-fatal condition might be fatal to the patient. One possible solution is to incorporate a ventricular defibrillator with an atrial defibrillator. However, the energy required for a ventricular defibrillation is significantly higher than that required for atrial fibrillation. Therefore, the capacitors and batteries needed for ventricular defibrillation are much larger and the device would need to be the same size as a conventional implantable cardiac ventricular defibrillator.
An alternate therapy for atrial defibrillation comprises drug injection devices. Numerous prior art devices disclose various types of implantable drug pumps which discharge an amount of drugs at the onset of atrial fibrillation.
While prior art methods and devices for attempting to stop atrial fibrillation have performed adequately, they continue to suffer from the drawbacks of potentially causing ventricular fibrillation, being large in size, and being very costly.